Answer:
Because of inertia.
Step-by-step explanation:
When a body is initially at rest and a force is applied in the forward direction, it shifts backwards before moving in the direction of the force. And when a body is in motion and a force is applied to halt it suddenly, it would shift forward. This force experienced by the body explains the principle of inertia.
Therefore, we move backwards when the jeep starts to moved because of inertia.